Many crude oils contain significant quantities of asphaltenes. It is desirable to remove the asphaltenes from the oil, because asphaltenes tend to solidify and foul subsequent processing equipment, and because removal of asphaltenes lowers the viscosity of the oil. Solvent extraction of asphaltenes is used to process residual crude that produces Deasphalted Oil (DAO) which is subsequently catalyticly cracked and made into predominantly diesel. The deasphalting process typically involves contacting a heavy oil with a solvent. The solvent is typically an alkane such as, propane to pentanes. The solubility of the solvent in the heavy oil decreases as the temperature increases. A temperature is selected wherein substantially all the paraffinic hydrocarbons go into solution, but where a portion of the resins and the asphaltenes precipitate. Because solubility of the asphaltenes is low in this solvent-oil mixture, the asphaltenes precipitate, and are separated from the oil.
Then high pressure steam or a fired heater is typically used to heat the deasphalted oil-solvent mixture to sufficient temperature. The oil portion then separates from the solvent without having to vaporize the solvent. This reduces energy consumption by about 20 to 30 percent over separating off and recovering the solvent for re-use.
The choice of solvent depends on the quality of the oil. As the molecular weight of the solvent increases, the amount of solvent needed decreases but the selectivity, for example to resins and aromatics, decreases. Propane requires more solvent but also does not extract as much aromatics and resins. Solvent recovery costs are generally greater with lower molecular weight solvents.
The process and advantages of gasifying hydrocarbon material into synthesis gas are generally known in the industry. Hydrocarbon materials that have been gasified include solids, liquids, and mixtures thereof. Gasification involves mixing an oxygen-containing gas at quantities and under conditions sufficient to cause the partial oxidation of the hydrocarbon material into carbon monoxide and hydrogen. The gasification process is very exothermic. Gas temperatures in the gasification reactor are often above 1100.degree. C. (2000.degree. F.). The hot synthesis gas is often quenched with water, and then a portion of the remaining sensible heat in the gas is used to make steam. There is a temperature at which steam generation is no longer feasible. Remaining heat in the gas is then typically released to the atmosphere via fan coolers.